Multiblade Fan

ABSTRACT

A multi-blade fan includes a spirally-shaped housing which has a bell-mouth orifice on one side, a sucking inlet and an exhausting outlet, an impeller which is placed in a housing and has a plurality of blades supported by a main plate and a lateral plate at both the axial ends, and a motor for driving the impeller. A cross section, cut along vertically with respect to a rotary shaft of the impeller, of each one of the blades has a given shape which allows a main air stream to flow along a back face of each one of blades.

TECHNICAL FIELD

The present invention relates to multi-blade fans to be used inventilating blowers, air-conditioners, dehumidifiers, humidifiers,air-cleaners and so on.

BACKGROUND ART

Conventional multi-blade fans used in homes or offices are disclosed in,e.g. Unexamined Japanese Patent Publication No. 2002-168194. One ofthese conventional multi-blade fans is described hereinafter withreference to FIG. 12 and FIG. 13.

FIG. 12 shows a general view of a conventional multi-blade fan, of whichspirally-shaped housing 1 has bell-mouth orifice 2 on the upper side atthe center. Housing 1 also has sucking inlet 3 and exhausting outlet 4.Housing 1 includes impeller 5 therein, which is driven by motor 6.Impeller 5 has a number of blades 9 supported by main plate 7 andlateral plate 8 at both the axial ends of respective blades. Air suckedfrom inlet 3 works as inflow stream 10 as the arrow mark in FIG. 12shows and is guided to impeller 5.

FIG. 13 shows a sectional view cut along the direction vertical withrespect to the rotary shaft of blades 9. A number of blades 9 inidentical shape are annularly arranged at equal intervals. Each one ofblades 9 shapes like as shown in FIG. 13, and has leading edge 11,trailing edge 12, and protrusion 14 on back face 13.

The air guided by orifice 2 flows like inflow stream 10 and exhaustingstream 15 marked with the arrow marks. Separation vortices from backface 13 are suppressed by protrusion 14, thereby generating smallervortices, which lower turbulent noise.

In the conventional multi-blade fan, however, blades 9 of impeller 5still generate large vortices, so that the noise generated by impeller 5is not yet satisfactorily suppressed, and needs to be lowered.

DISCLOSURE OF INVENTION

The present invention addresses the problem discussed above, and aims toprovide a multi-blade fan generating lower noise. The multi-blade fan ofthe present invention thus comprises the following elements:

-   -   a spirally-shaped housing having a bell-mouth orifice at one        side, a sucking inlet, and an exhausting outlet;    -   an impeller placed in the housing and having a plurality of        blades which are supported by a main plate and a lateral plate        at both the axial ends of respective blades; and    -   a motor for driving the impeller.        Each one of the blades has a cross section cut in a given length        along the direction vertical with respect to its rotary shaft,        which cross section shows a given shape, which allows a main air        stream to flow along a back face of the blade.

The foregoing structure allows the multi-blade fan of the presentinvention to suppress the separation vortices generated on the back faceof the blade, thereby lowering the noise to be radiated outside.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a general view of a multi-blade fan in accordance with afirst embodiment of the present invention.

FIG. 2 shows a sectional view cut along the vertical direction withrespect to the rotary shaft of the blades of the multi-blade fan shownin FIG. 1.

FIG. 3 shows a sectional view cut along the vertical direction withrespect to the rotary shaft of the blades of the multi-blade fan inaccordance with a second embodiment of the present invention.

FIG. 4 shows a perspective view illustrating a main part of amulti-blade fan in accordance with a third embodiment of the presentinvention.

FIG. 5 shows a perspective view illustrating a main part of amulti-blade fan in accordance with a fourth embodiment of the presentinvention.

FIG. 6 shows a perspective view illustrating a main part of amulti-blade fan in accordance with a fifth embodiment of the presentinvention.

FIG. 7 shows a perspective view illustrating a main part of amulti-blade fan in accordance with a sixth embodiment of the presentinvention.

FIG. 8 shows a perspective view illustrating a main part of amulti-blade fan in accordance with a seventh embodiment of the presentinvention.

FIG. 9 shows a perspective view illustrating a main part of amulti-blade fan in accordance with an eighth embodiment of the presentinvention.

FIG. 10 shows a sectional view of a multi-blade fan in accordance with aninth embodiment of the present invention.

FIG. 11 shows a sectional view of a multi-blade fan in accordance with atenth embodiment of the present invention.

FIG. 12 shows a general view of a conventional multi-blade fan.

FIG. 13 shows a sectional view cut along the vertical direction withrespect to the rotary shaft of the blades of the conventionalmulti-blade fan shown in FIG. 12.

DESCRIPTION OF REFERENCE MARKS

-   21 housing-   22 orifice-   23 sucking inlet-   24 exhausting outlet-   25, 25 a, 25 b, 25 c, 25 d, 25 e, 25 f, 25 g impeller-   26 motor-   27 main plate-   28 lateral plate-   29, 29 a, 29 b, 29 c, 29 d, 29 e, 29 f, 29 g blade-   31, 31 a, 31 b, 31 c, 31 d, 31 e, 31 f, 31 g leading edge-   32, 32 a, 32 b, 32 c, 32 d, 32 e, 32 f, 32 g trailing edge-   33, 33 a, 33 b, 33 c, 33 d, 33 e, 33 f, 33 g back face-   36, 36 a, 36 b, 36 c, 36 d, 36 e, 36 f, 36 g thin walled section-   37, 37 a, 37 b, 37 c, 37 d, 37 e, 37 f, 37 g thick walled section-   38, 38 a, 38 b, 38 c, 38 d, 38 e, 38 f, 38 g junction-   40 first orifice-   41, 44 second orifice

PREFERRED EMBODIMENTS OF INVENTION

Exemplary embodiments of the present invention are demonstratedhereinafter with reference to the accompanying drawings.

Embodiment 1

FIG. 1 shows a general view of a multi-blade fan in accordance with thefirst embodiment of the present invention. Spirally-shaped housing 21has bell-mouth orifice 22 on the upper side at the center, sucking inlet23, and exhausting outlet 24. Housing 21 includes impeller 25 therein,which is driven by motor 26. Impeller 25 has a number of blades 29supported by main plate 27 and lateral plate 28 at both the axial endsof respective blades. Air sucked from inlet 23 works as inflow stream 30and guides the air supplied to impeller 25 along the arrow marks shownin FIG. 1.

FIG. 2 shows a sectional view cut along the direction vertical withrespect to the rotary shaft of blades 29 of the multi-blade fan shown inFIG. 1. A number of blades 29 in identical shape are annularly arrangedat equal intervals. Each one of blades 9 shapes like as shown in FIG. 2,and has leading edge 31, trailing edge 32, back face 33 each of whichare in given shapes.

The air guided by orifice 22 flows along inflow stream 30 and exhaustingstream 35 marked with the arrow marks. Separation vortices at back face33 are suppressed by the given shape of back face 33, thereby generatingsmaller vortices, which reduce turbulent noise.

Next, the shape of respective blades 29 is detailed hereinafter. Motor26 drives impeller 25 to rotate along arrow mark R, then airflow alongback face 33 of blade 29 separates from the midway of blade 29.Separation vortices grow greater as the airflow approaches to the outerperiphery, and grows to the maximum size at an exhausting outlet ofblade 29, so that generated turbulent noise tends to become loud.

However, back face 33 of blade 29 is shaped in a given contour so thatthe main air-stream can flow from leading edge 31 toward trailing edge32 along back face 33 of blade 29. To be more specific, a cross sectionof back face 33 cut along the direction vertical with respect to therotary shaft of blade 29 has the given contour, namely, the contourincludes thin-walled section 36 and thick-walled section 37 from leadingedge 31 to trailing edge 32.

The thickness of thin-walled section 36 is not less than 1/10 (onetenth, or 10%) that of thick-walled section 37 and not greater than ½(one half, or 50%) thereof. The length of thin-walled section 36 is notshorter than 1/20 and not longer than ⅓ of the chord length. Junction 38between thin-walled section 36 and thick-walled section 37 shapes likean arc, and the length of junction 38 is not shorter than 1/20 and notlonger than 1/10 of the chord length. The arc-shaped junction 38preferably has a contour that assists section 36 to change rathersharply over to section 37.

The shape discussed above allows suppressing the separation of airflowfrom back face 33, so that vortices separating from back face 33 becomesmaller. The reason why thick-walled section 37 is placed at a distancefrom leading edge 31 is that the separation vortices occur at a placesome few distance away from leading edge 31. If the thickness ofthick-walled section 37 is too thick, intervals between adjacent bladesbecome smaller, while if it is too thin, the expected advantage cannotbe produced. The foregoing range is thus optimum. As a result,separation vortices at blade 29 are reduced, so that the noise generatedby the impeller can be lowered.

Embodiment 2

FIG. 3 shows a sectional view cut along the direction vertical withrespect to the rotary shaft of blade 29 a of the multi-blade fan inaccordance with the second embodiment of the present invention. Elementssimilar to those in the first embodiment have the same reference marks,and the detailed descriptions thereof are omitted here.

The air guided by orifice 22 flows along inflow stream 30 a andexhausting stream 35 a marked with the arrow marks. Separation vorticesat back face 33 a are suppressed by the given shape of back face 33 a,thereby generating smaller vortices, which lower turbulent noise.

As shown in FIG. 3, back face 33 a of blade 29 a is shaped in a givencontour so that the main air stream can flow from leading edge 31 atoward trailing edge 32 a along back face 33 a of blade 29 a. To be morespecific, a cross section of back face 33 a cut along the directionvertical with respect to the rotary shaft of blade 29 a has the givencontour, namely, the contour includes thin-walled section 36 a andthick-walled section 37 a, which tapers, i.e. becomes thinner, towardtrailing edge 32 a. The thickness of trailing edge 32 a is about a halfof the thickness around junction 38 a.

The thickness of thin-walled section 36 a is not less than 1/10 of themax. thickness of thick-walled section 37 a and not greater than ½thereof. The length of thin-walled section 36 a is not shorter than 1/20and not longer than ⅓ of the chord length. Junction 38 a betweenthin-walled section 36 a and thick-walled section 37 a shapes like anarc, and the length of junction 38 a is not shorter than 1/20 and notlonger than 1/10 of the chord length. The arc-shaped junction 38 apreferably has a contour that assists section 36 a to change rathersharply over to section 37 a.

In this second embodiment, back face 33 a has a cross section cut alongthe direction vertical with respect to the rotary shaft of blade 29 a,and the cross section changes in its thickness firstly thicker thenthinner gradually from leading edge 31 a toward trailing edge 32 a. Thisstructure suppresses the separation of the airflow from the back face,and allows the airflow to flow smoothly toward the trailing edge. Thereason why thick-walled section 37 a is placed at a distance fromleading edge 31 a is that the separation vortices occur at a place somefew distance away from leading edge 31 a. If the thickness ofthick-walled section 37 a is too thick, intervals between adjacentblades become smaller, while if it is too thin, the expected advantagecannot be produced.

The main air stream, in general, encounters greater separation vorticesat a some few distance away from the inlet, and then the vorticesgradually become smaller. The thickness tapers toward the outlet inaccordance with this mechanism, thus the main air stream is not hinderedand can be efficiently guided to the outlet. As a result, the separationvortices from blade 29 a become smaller, so that the noise generated bythe impeller can be lowered.

Embodiment 3

FIG. 4 shows a perspective view illustrating a main part of amulti-blade fan in accordance with the third embodiment of the presentinvention. Elements similar to those in the first and the secondembodiments have the same reference marks, and the detailed descriptionsthereof are omitted here.

As shown in FIG. 4, impeller 25 b includes a number of blades 29 bsupported by main plate 27 b and lateral plate 28 b at both the axialends of each one of blades 29 b, which are formed in a given shapewithin given length L1 axially from main plate 27 b. Length L1 fallswithin a range from not shorter than ⅓ to not longer than ⅔ of theentire axial length of blade 29 b.

The given shape within given length L1 is similar to that of the firstembodiment; a contour of the back face includes thin-walled section 36 band thick-walled section 37 b from leading edge 31 b to trailing edge 32b. The thickness of thin-walled section 36 b is not less than 1/10 thatof thick-walled section 37 b and not greater than ½ thereof. The lengthof thin-walled section 36 b is not shorter than 1/20 and not longer than⅓ of the chord length. Junction 38 b between thin-walled section 36 band thick-walled section 37 b shapes like an arc, and the length ofjunction 38 b is not shorter than 1/20 and not longer than 1/10 of thechord length. The arc-shaped junction 38 b preferably has a contour thatassists section 36 b to change rather sharply over to section 37 b.

The foregoing shape of blade 29 b allows suppressing the separation ofairflow from the lateral-face and the back-face of main plate 27 b whenthe airflow gathers on main plate 27 b, i.e. at a greater airflow volumetime. The reason why thick-walled section 37 b is placed at a distancefrom leading edge 31 b is that the separation vortices occur at a placesome few distance away from leading edge 31 b. If the thickness ofthick-walled section 37 b is too thick, intervals between adjacentblades become smaller, while if it is too thin, the expected advantagecannot be produced.

The foregoing structure allows the airflow around the back face to flowalong blade 29 b efficiently, so that the separation vortices can besuppressed, thus the noise generated by the impeller can be lowered.

Embodiment 4

FIG. 5 shows a perspective view illustrating a main part of amulti-blade fan in accordance with the fourth embodiment of the presentinvention. Elements similar to those in the first through the thirdembodiments have the same reference marks, and the detailed descriptionsthereof are omitted here.

As shown in FIG. 5, impeller 25 c includes a number of blades 29 csupported by main plate 27 c and lateral plate 28 c at both the axialends of each one of blades 29 c, which are formed in a given shapeaxially within given length L2 from main plate 27 c. Length L2 fallswithin a range from not shorter than ⅓ to not longer than ⅔ of theentire axial length of blade 29 c.

The given shape within given length L2 is similar to that of the secondembodiment; a contour of the back face includes thin-walled section 36 cand thick-walled section 37 c from leading edge 31 c to trailing edge 32c. Thick-walled section 37 c gradually becomes thinner toward trailingedge 32 c, and the thickness of trailing edge 32 c is about a half ofthe thickness around junction 38 c.

The thickness of thin-walled section 36 c is not less than 1/10 of themax. thickness of thick-walled section 37 c and not greater than ½thereof. The length of thin-walled section 36 c is not shorter than 1/20and not longer than ⅓ of the chord length. Junction 38 c betweenthin-walled section 36 c and thick-walled section 37 c shapes like anarc, and the length of junction 38 c is not shorter than 1/20 and notlonger than 1/10 of the chord length. The arc-shaped junction 38 cpreferably has a contour that assists section 36 c to change rathersharply over to section 37 c.

The foregoing shape of blade 29 c allows suppressing the separation ofairflow from main plate 27 c when the airflow gathers on main plate 27c, i.e. at a greater airflow volume time, and allows the airflow to flowsmoothly toward trailing edge 32 c. The reason why thick-walled section37 c is placed at a distance from leading edge 31 c is that theseparation vortices occur at a place some few distance away from leadingedge 31 c. If the thickness of thick-walled section 37 c is too thick,intervals between adjacent blades become smaller, while if it is toothin, the expected advantage cannot be produced.

The foregoing structure allows the airflow around the back face to flowalong blade 29 c efficiently, and the separation vortices can be furthersuppressed, thus the noise generated by the impeller can be lowered.

Embodiment 5

FIG. 6 shows a perspective view illustrating a main part of amulti-blade fan in accordance with the fifth embodiment of the presentinvention. Elements similar to those in the first through the fourthembodiments have the same reference marks, and the detailed descriptionsthereof are omitted here.

As shown in FIG. 6, impeller 25 d includes a number of blades 29 dsupported by main plate 27 d and lateral plate 28 d at both the axialends of each one of blades 29 d, which are formed in a given shapewithin given length L3 axially from lateral plate 28 d. Length L3 fallswithin a range from not shorter than ⅓ to not longer than ⅔ of theentire axial length of blade 29 d.

The given shape within given length L3 is similar to that of the firstembodiment; a contour of the back face includes thin-walled section 36 dand thick-walled section 37 d from leading edge 31 d to trailing edge 32d. The thickness of thin-walled section 36 d is not less than 1/10 thatof thick-walled section 37 d and not greater than ½ thereof. The lengthof thin-walled section 36 d is not shorter than 1/20 and not longer than⅓ of the chord length. Junction 38 d between thin-walled section 36 dand thick-walled section 37 d shapes like an arc, and the length ofjunction 38 d is not shorter than 1/20 and not longer than 1/10 of thechord length. The arc-shaped junction 38 d preferably has a contour thatassists section 36 d to change rather sharply over to section 37 d.

The foregoing shape of blade 29 d allows suppressing the separation ofairflow from lateral plate 28 d when the airflow gathers on lateralplate 28 d, i.e. at a lower airflow volume time, and allows the airflowto flow smoothly toward trailing edge 32 d. The reason why thick-walledsection 37 d is placed at a distance from leading edge 31 d is that theseparation vortices occur at a place some few distance away from leadingedge 31 d. If the thickness of thick-walled section 37 d is too thick,intervals between adjacent blades become smaller, while if it is toothin, the expected advantage cannot be produced.

When the airflow gathers on lateral plate 28 d, i.e. at the low airflowvolume time, the foregoing structure allows the airflow around the backface to flow along blade 29 d efficiently, and the separation vorticescan be suppressed, thus the noise generated by the impeller can belowered.

Embodiment 6

FIG. 7 shows a perspective view illustrating a main part of amulti-blade fan in accordance with the sixth embodiment of the presentinvention. Elements similar to those in the first through the fifthembodiments have the same reference marks, and the detailed descriptionsthereof are omitted here.

As shown in FIG. 7, impeller 25 e includes a number of blades 29 esupported by main plate 27 e and lateral plate 28 e at both the axialends of each one of blades 29 e, which are formed in a given shapewithin given length L4 axially from lateral plate 28 e. Length L4 fallswithin a range from not shorter than ⅓ to not longer than ⅔ of theentire axial length of blade 29 e.

The given shape within given length L4 is similar to that of the secondembodiment; a contour of the back face includes thin-walled section 36 eand thick-walled section 37 e from leading edge 31 e to trailing edge 32e. Thick-walled section 37 e gradually becomes thinner toward trailingedge 32 e, and the thickness of trailing edge 32 e is about a half ofthe thickness around junction 38 e.

The thickness of thin-walled section 36 e is not less than 1/10 of themax. thickness of thick-walled section 37 e and not greater than ½thereof. The length of thin-walled section 36 e is not shorter than 1/20and not longer than ⅓ of the chord length. Junction 38 e betweenthin-walled section 36 e and thick-walled section 37 e shapes like anarc, and the length of junction 38 e is not shorter than 1/20 and notlonger than 1/10 of the chord length. The arc-shaped junction 38 epreferably has a contour that assists section 36 e to change rathersharply over to section 37 e.

The foregoing shape of blade 29 e allows suppressing the separation ofairflow from lateral plate 28 e when the airflow gathers on lateralplate 28 e, i.e. at a low airflow volume time, and allows the airflow toflow smoothly toward trailing edge 32 e. The reason why thick-walledsection 37 e is placed at a distance from leading edge 31 e is that theseparation vortices occur at a place some few distance away from leadingedge 31 e. If the thickness of thick-walled section 37 e is too thick,intervals between adjacent blades become smaller, while if it is toothin, the expected advantage cannot be produced.

When the airflow gathers on lateral plate 29 e, i.e. at the low airflowvolume time, the foregoing structure allows the airflow around the backface to flow along blade 29 e efficiently, and the separation vorticescan be further suppressed, thus the noise generated by the impeller canbe lowered.

Embodiment 7

FIG. 8 shows a perspective view illustrating a main part of amulti-blade fan in accordance with the seventh embodiment of the presentinvention. Elements similar to those in the first through the sixthembodiments have the same reference marks, and the detailed descriptionsthereof are omitted here.

As shown in FIG. 8, impeller 25 f includes a number of blades 29 fsupported by main plate 27 f, of which external shape is smaller thanthe main plates discussed previously, and lateral plate 28 f at both theaxial ends of each one of blades 29 f, which are formed in a given shapewithin given length L5 axially from lateral plate 28 f. Length L5 fallswithin a range from not shorter than ⅓ to not longer than ⅔ of theentire axial length of blade 29 f.

The given shape within given length L5 is similar to that of the firstembodiment; a contour of the back face includes thin-walled section 36 fand thick-walled section 37 f from leading edge 31 f to trailing edge 32f. The thickness of thin-walled section 36 f is not less than 1/10 thatof thick-walled section 37 f and not greater than ½ thereof. The lengthof thin-walled section 36 f is not shorter than 1/20 and not longer than⅓ of the chord length. Junction 38 f between thin-walled section 36 fand thick-walled section 37 f shapes like an arc, and the length ofjunction 38 f is not shorter than 1/20 and not longer than 1/10 of thechord length. The arc-shaped junction 38 f preferably has a contour thatassists section 36 f to change rather sharply over to section 37 f.

The foregoing shape of blade 29 f allows suppressing the separation ofairflow from lateral plate 28 f when the airflow gathers on lateralplate 28 f, i.e. at a low airflow volume time, and allows the airflow toflow smoothly toward trailing edge 32 f. The reason why thick-walledsection 37 f is placed at a distance from leading edge 31 f is that theseparation vortices occur at a place some few distance away from leadingedge 31 f. If the thickness of thick-walled section 37 f is too thick,intervals between adjacent blades become smaller, while if it is toothin, the expected advantage cannot be produced.

When the airflow gathers on lateral plate 28 f, i.e. at the low airflowvolume time, the foregoing structure allows the airflow around the backface to flow along blade 29 f efficiently, and the separation vorticescan be suppressed, thus the noise of the impeller can be lowered.

The seventh embodiment differs from the fifth embodiment in the diameterof main plate 27 f, to be more specific, the diameter of main plate 27 fis smaller than the diameter of thick-walled section 37 f. Thisstructure allows manufacturing impeller 25 f made of resin in a unitaryform. The unitary molding not only lowers the noise generated by theblades at the low airflow volume time but also reduces the cost ofmulti-blade fan.

Embodiment 8

FIG. 9 shows a perspective view illustrating a main part of amulti-blade fan in accordance with the eighth embodiment of the presentinvention. Elements similar to those in the first through the seventhembodiments have the same reference marks, and the detailed descriptionsthereof are omitted here.

As shown in FIG. 9, impeller 25 g includes a number of blades 29 gsupported by main plate 27 g, of which external shape is smaller thanthe main plates discussed above, and lateral plate 28 g at both theaxial ends of each one of blades 29 f, which are formed in a given shapewithin given length L6 axially from lateral plate 28 g. Length L6 fallswithin a range from not shorter than ⅓ to not longer than ⅔ of theentire axial length of blade 29 g.

The given shape within given length L6 is similar to that of the secondembodiment; a contour of the back face includes thin-walled section 36 gand thick-walled section 37 g from leading edge 31 g to trailing edge 32g. Thick-walled section 37 g gradually becomes thinner toward trailingedge 32 g, and the thickness of trailing edge 32 g is about a half ofthe thickness around junction 38 g.

The thickness of thin-walled section 36 g is not less than 1/10 of themax. thickness of thick-walled section 37 g and not greater than ½thereof. The length of thin-walled section 36 g is not shorter than 1/20and not longer than ⅓ of the chord length. Junction 38 g betweenthin-walled section 36 g and thick-walled section 37 g shapes like anarc, and the length of junction 38 g is not shorter than 1/20 and notlonger than 1/10 of the chord length. The arc-shaped junction 38 gpreferably has a contour that assists section 36 e to change rathersharply over to section 37 g.

The foregoing shape of blade 29 g allows suppressing the separation ofairflow from lateral plate 28 g when the airflow gathers on lateralplate 28 g, i.e. at a low airflow volume time, and allows the airflow toflow smoothly toward trailing edge 32 g. The reason why thick-walledsection 37 g is placed at a distance from leading edge 31 g is that theseparation vortices occur at a place some few distance away from leadingedge 31 g. If the thickness of thick-walled section 37 g is too thick,intervals between adjacent blades become smaller, while if it is toothin, the expected advantage cannot be produced.

When the airflow gathers on lateral plate 29 g, i.e. at the low air-flowtime, the foregoing structure allows the airflow around the back face toflow along blade 29 g efficiently, and the separation vortices can befurther suppressed, thus the noise generated by the impeller can belowered.

The eighth embodiment differs from the sixth embodiment in the diameterof main plate 27 g, to be more specific, the diameter of main plate 27 gis smaller than the diameter of thick-walled section 37 g. Thisstructure allows manufacturing impeller 25 g made of resin in a unitaryform. The unitary molding not only lowers the noise generated by theblades at the low airflow volume time but also reduces the cost ofmulti-blade fan.

Embodiment 9

FIG. 10 shows a sectional view illustrating a multi-blade fan inaccordance with the ninth embodiment of the present invention. Elementssimilar to those in the first through the eighth embodiments have thesame reference marks, and the detailed descriptions thereof are omittedhere.

Spirally-shaped housing 21 has bell-mouth orifice 40 on the upper sideat the center, sucking inlet 42 and exhausting outlet 43. Housing 21includes impeller 25 therein, which is driven by motor 26. Impeller 25has a number of blades 29 supported by main plate 27 and lateral plate28 at both the axial ends of respective blades. Air sucked from inlet 42works as inflow stream 30 and guides the air supplied to impeller 25along the arrow marks shown in FIG. 10.

In this ninth embodiment, second orifice 41 is added to outside of firstorifice 40, and diameter D1 of first orifice 40 and that of secondorifice 41 are the same. Interval L7 between these two orifices is notsmaller than 1/10 of diameter D1 or D2 and not greater than ½ of thediameter.

The noise generated by impeller 25 is radiated from the center of firstorifice 40 toward sucking inlet 42; however, the noise radiated outsideis cut off by second orifice 41 and attenuated between the two orificesdue to resonance, so that the noise radiated outside is lowered. Ifinterval L7 between the two orifices is too short, noise reductioneffect becomes smaller, and if interval L7 is too long, the effectreaches the max. at a certain length, however; interval L7 exceedingthat certain length, the effect starts lowering, and a device includingthis fan becomes bulky. The preceding range is thus preferable. Theforegoing structure allows lowering the noise radiated outside of themulti-blade fan.

Embodiment 10

FIG. 11 shows a sectional view illustrating a multi-blade fan inaccordance with the tenth embodiment of the present invention. Elementssimilar to those in the first through the ninth embodiments have thesame reference marks, and the detailed descriptions thereof are omittedhere.

The tenth embodiment differs from the ninth one in inner diameter D3 ofsecond orifice 44. Inner diameter D3 is smaller than inner diameter D1of first orifice 40 but not smaller than ⅔ of diameter D1. Interval L8between first orifice 40 and second orifice 44 is not smaller than 1/10of diameter D1 and not greater than ½ thereof.

The noise generated by impeller 25 is radiated from the center of firstorifice 40 toward sucking inlet 42; however, the noise radiated outsideis cut off by second orifice 44 and attenuated between the two orificesdue to resonance, so that the noise radiated outside is lowered. Sinceinner diameter D3 of second orifice 44 is smaller than inner diameter D1of first orifice 40, the radiated noise can be more effectively cut off,so that the noise radiated outside is further lowered. Greaternoise-reduction effect can be expected at the smaller inner diameter D3of second orifice 44; however, smaller inner diameter D3 will reduce anairflow volume, so that the preceding range of inner diameter D3 isoptimum. The structure discussed above allows further lowering the noiseradiated outside of the multi-blade fan.

Embodiment 11

The eleventh embodiment introduces a multi-blade fan in which one of theblade-shape oriented noise reduction structures described in firstthrough eighth embodiments is combined with one of the orifice-orientednoise reduction structures described in the ninth and tenth embodiments.To be more specific, although a drawing of this multi-blade fan isomitted here, one of impellers 25, 25 a, 25 b, 25 c, 25 d, 25 e, 25 f,25 g is incorporated into the structure described in the ninth or thetenth embodiment.

This structure allows the airflow on the back face of the blades to flowalong the blades, thereby suppressing the separation vortices, and yet,allows the second orifice to cut off the radiated noise, thereby furtherlowering the noise radiated outside effectively.

INDUSTRIAL APPLICABILITY

A multi-blade fan of the present invention includes an impeller formedof a number of blades, each one of which has a given shape of crosssection cut along the direction vertical with respect to the rotaryshaft of the impeller. The given shape allows a main air stream to flowalong the back face of the blade. This structure allows suppressingseparation vortices, and thus lowering the noise radiated outside.

1. A multi-blade fan comprising: a spirally-shaped housing including a bell-mouth orifice at one side, a sucking inlet and an exhausting outlet; an impeller disposed in the housing and including a plurality of blades supported by a main plate and a lateral plate at both axial ends of each one of the blades; and a motor for driving the impeller, wherein a cross section, cut along vertically with respect to a rotary shaft within a given length, of each one of the blades has a given shape which allows a main air stream to flow along a back face of each one of the blades.
 2. The multi-blade fan of claim 1, wherein the given length is an entire axial length of each one of the blades.
 3. The multi-blade fan of claim 1, wherein the given shape includes a change such that a thin-walled section of the back face changes over to a thick-walled section along from a leading edge to a trailing edge of each one of the blades.
 4. The multi-blade fan of claim 3, wherein a length of the thin-walled section is not shorter than 1/20 and not greater than ⅓ of a chord length.
 5. The multi-blade fan of claim 3, wherein a thickness of the thin-walled section is not smaller than 1/10 and not greater than ½ of a thickness of the thick-walled section.
 6. The multi-blade fan of claim 3, wherein a junction between the thin-walled section and the thick-walled section shapes like an arc, of which length is not shorter than 1/20 and not longer than 1/10 of a chord length.
 7. The multi-blade fan of claim 3, wherein a thickness of the thick-walled section becomes thinner gradually toward the trailing edge.
 8. The multi-blade fan of claim 1, wherein the given length is not shorter than ⅓ and not greater than ⅔ of an axial length of each one of the blades from the main plate.
 9. The multi-blade fan of claim 1, wherein the given length is not shorter than ⅓ and not greater than ⅔ of an axial length of the blades from the lateral plate.
 10. The multi-blade fan of claim 3, wherein the main plate has an external appearance smaller than an external shape of the thick-walled section.
 11. The multi-blade fan of claim 1, wherein the orifice is formed of a first orifice nearer to the impeller and a second orifice, and the two orifices are disposed with a given interval in between for cutting off sound.
 12. The multi-blade fan of claim 11, wherein the first orifice has an inner diameter not shorter than 8/10 and not greater than 1/1 of an inner diameter of the impeller.
 13. The multi-blade fan of claim 11, wherein the given interval is not shorter than 1/10 and not longer than ½ of an inner diameter of the first orifice.
 14. The multi-blade fan of claim 11, wherein the second orifice has a contour identical to a contour of the first orifice.
 15. The multi-blade fan of claim 11, wherein the second orifice has an inner diameter not smaller than ⅔ and not greater than 1/1 of an inner diameter of the first orifice. 